I also can tell you a lot more about mics for music than for podcasting, so take my two cents for what it’s worth
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If you don’t already have an audio interface that allows for an XLR or at least 1/4” connection, a USB mic like the Blue mentioned above will be your best bet.
If you do have an interface that you can plug an XLR cable into, you have a lot more options. For instance, MXL makes very affordable condenser mics in your price range that seem to get decent reviews. Also they have a ribbon mic for $100 USD :
http://pro-audio.musiciansfriend.com/product/MXL-MXL-R144-Ribbon-Microphone?sku=583081
I realize you’re not there yet, but if down the line you’re considering investing more into it, you may also start thinking about using a preamp (which in my experience add as much or more sonic quality (or lack thereof) to the sound) as well as a compressor to limit the dynamic range of your voice. Here’s a thought:
http://pro-audio.musiciansfriend.com/product/Shure-SM7B-Microphone-with-Switchable-Response?sku=270247
In tandem with:
http://pro-audio.musiciansfriend.com/product/Golden-Age-Project-Pre73-Preamp?sku=580975
$750 is a lot more than $100, but will give you pro sounding results.
All said and done, really it depends on your voice (male, female, deep, high ??) and your personal preference more than anything.